GC Leong: Summary of Coastal Landforms - Geography for UPSC CSE

Coastal Features of Erosion

1. Capes & Bays

• On exposed coasts, the continual action of waves on the rocks of varying resistance causes the coastline to be eroded irregularly.
• This is particularly pronounced where hard rocks occur in alternate band with softer rocks.
• The softer rocks are worn back into inlets or bays & the harder ones persist as headlands or capes.
• Even where the coastline consists of one rock type, irregularities will be caused by variation within the rock.

2. Cliffs & Wave cut platforms

• Generally, any steep rock platform adjoining the coast forms a cliff, whose rate of recession will depend on its geological structure.
• Means the ______ & their resistance to wave attack.
• If the bed dips seaward, large blocks of rock will be dislodged & fall into the sea & cliff will rise in a series of steps.
• On the other hand, if the beds dip landward, the cliff will be more resistant to wave erosion.
• At the base of the cliff the sea cuts a notch, which gradually undermines the cliff, so that it collapses.
• As the cliff recedes landwards under the pounding of waves, an eroded base is left behind called a wave cut platform.
• The platform, upper part of which is exposed at low tides, slopes gently seawards, with its surface strewn with rock debris from the receding cliff.
• Further the abrasion continues until the pebbles are swept away in the sea with eroded material deposited on off shore terrace.

3. Cave, Arch, Stack & Stump

• Prolonged waves attack on the base of the cliff & excavate holes in regions of local weakness called ______
• When 2 caves approach each other from either side of headland & unite, they form an ______
• Further erosion by waves will lead to total collapse of the arch.
• The seaward portion of the headland will remain as a pillar of rock known as______
• With the course of time, these stubborn stacks will gradually be eroded, leaving behind the stumps, which are only just visible above the sea level.

4. Geos & Gloups (blow-holes)

• The occasional splashing of the waves against the roof of a cave may enlarge the joints when air is compressed & released repeatedly inside them.
• A natural shaft is thus formed which may eventually pierce through the surface.
• Waves breaking into the cave may force water or air out of this hole. Such a shaft is termed as Gloup or blow hole.
• The enlargement of blow-holes & continual action of waves weakens the cave roof.
• When the cave roof collapses, a long, narrow creek may develop known as Geos.

1. Beaches

• Sands & gravel loosened from the land are moved by waves to be deposited along the shore as beaches.
• The eroded material is transported along the shore in several distinct ways.
• Long shore drifts which comes obliquely to the coast carries material along the shore in the direction of the dominant wind.
• At the same time, backwash removes part of the material seawards, along the bed of the sea, & deposits it on the off-shore terrace & even beyond.
• The constant action of the waves automatically sorts out the shoreline deposits in a graded manner.
• The coarser materials are dropped by the waves at the top of the beaches & the finer materials, carried down the beach by the backwash, are dropped closer to the sea.

2. Spits & Bars

• The debris eroded by waves is continually moved by long shore drift & where there is indentation in the coast, such as at the mouth of the river or a bay; material may continue to be deposited across the inlet.
• As more materials are added, they will pile up into a ridge or embankment of shingle forming a spit, with one end attached to the land & other projecting into the sea.
• When a ridge of shingle is formed across the mouth of a river or the entrance to a bay, it is called a bar.
• Such a connecting bar that joins two land masses is known as Tombolo.

3. Marine Dunes & Dune Belts

• With the force of on-shore winds, a large amount of coastal sand is driven landwards forming extensive marine dunes that stretches into dune belts.
• Their advance inland may engulf farms, roads & even the entire villages;
• Hence to arrest the migration of dunes, sand-binding species of grass & shrubs, such as marram grass & pines are planted.

Types of Coasts

Despite a great variety of coastal features, coastlines may be divided into two basic types:

1. Coastline of Submergence

• Formed due to sinking of the land or rise of the sea.
• Including such coasts are Ria coasts, Fjord coasts, Estuarine coasts & Dalmatian/Longitudinal coasts.

2. Coastline of Emergence

• Formed due to the uplift of the land or fall in the sea level.
• Generally less common & include uplifted low land coast & emergent upland coast.

Coastline of Submergence

1. Ria Coasts - Drowned river valleys

• During the ice age, a great deal of water was locked up in the ice, which melted as the climate got wanner leading to increase in sea level.
• In upland coastal regions, where the mountain runs at right angle to the sea i.e. transversely to the coast, a rise in the sea level submerges or drowns the lower parts of the valleys to form long narrow branching inlets separated by narrow headlands.
• Hence, a raise a coastal inlet formed by the partial submergence of an unglaciated river valley that remains open to the sea & is a coastline having several parallel rias separated by prominent ridges, extending a distance inland.
• The drowning of river valleys along a stretch of coast and formation of rias results in an extremely irregular and indented coastline.
• A ria coast differ from the fiords in two ways viz. they are not glaciated, & their depth increases seaward.
• All rias are generally backed by highlands & support few large commercial ports & extensively used for sitting fishing ports & naval bases.

2. Fjord coasts - Drowned glaciated valleys

• Fjords were created by glaciers that moved very slowly over time, and greatly altered the landscape once they have moved through an area carving deep valley.
• Above process is called glaciation.
• Fjord is formed when a glacier retreats, after carving its typical U-shaped valley with the sea filling the resulting valley floor.
• It forms a narrow, steep sided inlet connected to the sea
• The terminal moraine pushed down the valley by the glacier is left underwater at the fjord’s entrance.
• It causes the water at the neck or mouth of the fjord to be shallower than the main body of the fjord behind it.
• Hence the opening toward the sea is often shallow & termed as threshold.

3. Dalmatian coasts

• A longitudinal coast where the mountains run parallel to the coast
• Where the submergence of the coastline produces long, narrow inlets with a chain of islands parallel to the coast.
• The elongated islands are the crests of former ranges & the narrow inlets were the former longitudinal valleys.
• Like ria and fiord coasts, the mountainous nature of Dalmatian coastline hinders inland communication.

4. Estuarine Coasts

• Estuarine coasts are basically the coasts made by estuaries, with streams of river freely flowing into the sea, making them excellent sites for the ports.
• An estuary is a partly enclosed coastal body of brackish water (salinity in between saline sea water & fresh river water) with one or more rivers or streams flowing into it, and with a tree connection to the open sea.
• Estuaries form a transition zone between river environments and maritime environments.
• They are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment.

COASTLINE OF EMERGENCE

• The uplifted part of continental self produces gently sloping coastal lowland.
• The offshore waters are shallow with the lagoons, salt marshes & mudflats.
• Where the emerging deposits from the continental shelf are sandy & gravelly, beaches & marine dunes are formed.
• Ports that were once located on the former coast, became inland towns.

2. Emergent upland coasts

• Faulting & earth movement may thrust up coastal plateaus so that whole region is raised forming a raised beach.
• A raised beach is beyond the range of waves, though it may still possess arches, stacks & other coastal features.
• The emergent upland coast is quite straight with steep cliffs & deeper off shore waters.